Conference meetings and classroom presentations have sometimes been recorded in an audio/visual (A/V) format. In the past, film cameras used photographic film, which had to be chemically developed for the images and synchronized with the audio track to become available for viewing. Camcorders have been made available more recently; these employ magnetic tape to store analog A/V. The recorded events can be played back after the tape has been rewound. However, tape editing can be labor-intensive, and the tape may not be reviewed until the recording is completed.
More recently, the introduction of the digital camera has further facilitated portability and convenience for A/V recordings that do not require motion-picture video. Consumer demand has reduced the prices for digital cameras. Pre-programming of the recording sequence is available either directly or through website control. The received video may be supplied by an inexpensive optical lens and low-pass filter to focus the light onto typically one charge-coupled device (CCD) or a prism with three such image sensors. Digital cameras typically have sixty-four grey levels or thirty-two levels of red-green-blue (RGB) color with 320×240 pixel resolution at about ten frames per second digitally transmitted via a serial or parallel port to a computer. Such digital cameras may use lossy compression to reduce the memory requirements for storing the images such as developed under the Joint Photographers Expert Group (JPEG) standard.
A digital camera typically includes a liquid crystal diode (LCD) display to view the image in real-time (contemporaneous with recording) for monitoring the image quality. The LCD display provides visual feedback for focal-stop aperture setting, lens focusing, background cropping, etc. Subsequent playback may be provided by connecting the digital camera to a television set. Television receivers are generally compliant with either the National Television Systems Committee (NTSC) standard in North America, or the Phase Alternating Line (PAL) standard. Alternatively, the image may be played back on a personal computer (PC) through a PC attachment (PC-ATA) interface.
The video information may be represented by pixels having either RGB or YUV component values. In the YUV, brightness or luminance is denoted by Y, and chromance by U and V, where U may be represented as B−Y (blue minus luminance) and V as R−Y (red minus luminance). A video decoder may format video data for display under one of a commonly used set of sampling frequencies, which are described as multiples of 3.75 MHz, the lowest common frequency for NTSC and PAL. For example, a 4:2:0 system digitizes Y at sampling frequency of 13.5 MHz, while U and V are sampled at 6.75 MHz every other line. A 4:4:4 system samples the luminance and color channels all at 13.5 MHz.
A system block diagram of a commercially available digital camera chip is presented in FIG. 1. This example is available from LSI Logic Corporation of Milpitas, Calif. The digital camera (dcam) device 10 of the depicted example is designed to receive an image 12. The camera lens 14 focuses the image 12 for the photons to be counted in the CCD 16. The image is digitally converted by the analog-to-digital converter (ADC) 18. The ADC 18 produces an input signal 20 to the CCD pre-processor 22 in the digital camera device 10.
The pre-processor 22 transmits data to several interconnected components including a JPEG coder/decoder (codec) 24, a 10-channel direct memory access (DMA) controller 26, a memory controller 28, a PC-ATA interface 30, general purpose input/output (I/O) interface 32, a serial I/O interface 34, and an on-screen display controller 36. The display controller 36 controls a LCD video controller 38 and a NTSC/PAL encoder 40 with a video digital-to-analog converter (DAC) 42.
The memory controller 28 may retrieve processing instructions stored in dynamic random access memory (DRAM) 44 and/or read-only memory (ROM) 46. The PC-ATA interface 30 may be associated with flash memory 48 or PC card, in which the received image 12 may be stored for subsequent retrieval. The LCD controller may be connected to the camera's LCD display 50 to provide immediate visual feedback to the digital camera operator. As an alternative to the small screen provided by the LCD display 50, the serial I/O 34 may be linked to a PC interface 52 attached to a video monitor. The video DAC 42 may be connected to a television set 54 or other monitor as an alternative A/V display device.
The introduction of the reduced instruction set computer (RISC) has facilitated processing for some applications. The dcam device 10 may be controlled by a central mini-RISC microprocessor 56. Image rendering may be performed by a pixel coprocessor 58. A single-cycle multiplier/accumulator 60 may support auxiliary image processing. Real-time operating systems for A/V embedded application processing in RISC chips include Nucleus, pSOS and VxWorks. Nucleus is available from Accelerated Technology Inc. of Mobile, Ala.; pSOS is available from Gespas, Inc. of Mesa, Ariz.; VxWorks is available from Wind River Systems of Alameda, Calif.
Current digital cameras have a number of drawbacks, however. Recording parameters such as the image capture interval and pixel resolution must be decided ahead of time using pre-programmed instructions, thereby limiting operational flexibility. Also, digital cameras do not permit simultaneous playback during the recording process. After the A/V recording has begun, a person arriving late to the presentation cannot review the previous exchanges without interrupting the ongoing recording of the current proceedings.
Memory usage in a digital camera is not optimized to maximize a particular feature, such as record duration. Typically, the user must resolve competing issues manually to most efficiently utilize the available memory. If during a presentation, an important image should be recorded, an earlier lower priority image cannot be easily overwritten. Instead, additional memory must be provided until it is consumed.
Editing can be performed only after the recording has been completed. In order to create multiple versions of the A/V record to disseminate to separate destinations, several copies of the recorded source data are needed, with the attendant costs in additional equipment and time devoted to playback and editing.